Blood is a major tissue of the human body, and has as a predominant role the delivery of oxygen from the lungs to peripheral tissues. This role is carried out by erythrocytes, i.e., red blood cells (RBC). The oxygen is furnished to the peripheral cells by an exchange-diffusion system brought about in the lungs in a red, iron-containing protein called hemoglobin. When hemoglobin combines with oxygen, oxyhemoglobin is formed and after oxygen is given up by the tissues, the oxyhemoglobin is reduced to deoxyhemoglobin.
The red cell membrane is composed of two major structural units, the membrane bilayer and a cytoskeleton. A lipid bilayer and integral membrane proteins form the membrane bilayer, which has little structural strength and fragments readily by vesiculation. The other major component, the membrane skeleton, stabilizes the membrane bilayer and provides resistance to deformation. The cytoskeleton is linked to the bilayer in the erythrocyte membrane, possibly by lipid-protein as well as protein-protein associations. The hemoglobin, and other RBC components, are contained within the red cell membrane.
In adults, bone marrow is active in the formation of new red blood cells. Once erythrocytes enter the blood, they have an average lifetime of about 120 days. In an average person, about 0.83% of the erythrocytes are destroyed each day by phagocytosis, hemolysis or mechanical damage in the body, and the depleted cells are renewed by the bone marrow.
A wide variety of injuries and medical procedures require the transfusion of whole blood or a variety of blood components. Every patient does not require whole blood and, in fact, the presence of all of the blood components can cause medical problems. Separate blood fractions can be stored under those special conditions best suited to assure their biological activity at the time of transfusion. For example, when donor blood is received at a processing center, erythrocytes are separated and stored by various methods. Such cells are storable in citratephosphate-dextrose at 4.degree. C. for up to five weeks, generally as a unit of packed erythrocytes having a volume of from 200 to 300 ml and a hematocrit value (expressed as corpuscular volume percent) of 70 to 90.
Erythrocytes may also be frozen at from -30.degree. C. to 196.degree. C. and stored for up to seven years in a glycerol solution, but must be kept frozen at low temperatures in order to survive sufficiently for transfusion. Both these methods require careful maintenance of storage temperature to avoid disruption of the desired biological activity of the erythrocytes, and must meet the American Association of Blood Bank (AABB) standard of survival of 80-85% of the thawed cells. After thawing the cells must be washed to remove the glycerol, which is a time and cost disadvantage.
It has thus been a desideratum to obtain a method for the storage of red blood cells which does not require the washing of the thawed cells prior to transfusion. Such a method would facilitate the rapid availability of erythrocytes for medical purposes.
One such desired method has been the freezing of red blood cells, since such cells could be stored and easily reconstituted for use in mammals.